A wide variety of guidewires are used for various medical purposes in the treatment of the human body. Among the more common uses is in blood vessels to guide a catheter to a site within the patient's blood vessel to perform the procedure for which the catheter is adapted. For example, guidewires, particularly small diameter steerable guidewires perform an important function in percutaneous transluminal coronary angioplasty. Illustrative of such guidewires are those described in U.S. Pat. No. 4,545,390 (Leary) and U.S. Pat. No. 4,538,622 (Samson). Each of the guidewires described in those patents has a torsionally rigid, longitudinally flexible shaft and a flexible distal end that includes a coil, all or part of which is radiopaque so that the physician can monitor fluoroscopically the position and advancement of the guidewire in the patient's blood vessel. In procedures, such as coronary angioplasty, in which a catheter is advanced through the patient's arteries, it often is the practice to inject a radiopaque contrast liquid into the artery so that the shape and path of the artery may be visualized fluoroscopically. The radiopacity of the guidewire coil may be so dense as to visually obstruct part of the artery which the physician may desire to view when the contrast liquid is injected. For use in such instances, it would be desirable for the guidewire to be only partially radiopaque, that is, to form a light but visible grey shadow in some portions and a heavy, dark fluoroscopic image on another.
It also is desirable in the design of guidewires to coat the coil with a low friction material so as to reduce friction between the guidewire and catheter.
It is among the general object of the invention to provide guidewires having the foregoing desirable characteristics.